forked from Mirrors/opensbi

pmpcfg_csr and pmpcfg_shift are only negative for an unexpected value of __riscv_xlen. We can immediately return in this case. Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com> Reviewed-by: Dong Du <Dd_nirvana@sjtu.edu.cn> Reviewed-by: Anup Patel <anup.patel@wdc.com>